1. Field
The invention relates to optical communication equipment and, more specifically but not exclusively, to constellations that can be used to encode data at a transmitter and decode the corresponding modulated optical signals at a receiver.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Constellations that encode four bits per symbol are of special interest to optical transport systems, e.g., because these constellations offer a good compromise between spectral efficiency and maximum achievable transmission distance. One example of such a constellation is a square 16-QAM (quadrature-amplitude-modulation) constellation. Although this constellation can provide good performance characteristics when used for optical channels in which the noise is dominated by additive white Gaussian noise (AWGN), it does not perform as well when used for data transmission over optical channels in which the noise has a significant non-AWGN component.